1. Field of the Invention
This invention relates to brakes used in elevators and, in particular, to a brake that applies a braking force directly to an elevator sheave and that is configured for use in existing elevators without requiring modification of the elevators.
2. Discussion of Related Art
A conventional elevator includes an elevator car and a counterweight disposed within an elevator shaft at opposite ends of a plurality of cables. Portions of each cable intermediate the elevator car and the counterweight are disposed within grooves formed in the circumference of a sheave that is located above the elevator car and counterweight and is rotatably driven by a motor to control the ascent and descent of the elevator car. One or more gears may be disposed between the motor and sheave or the sheave may be directly rotated by the motor. The sheave, motor, and any motor controls may be located within a control room above the elevator shaft or within the elevator shaft itself. The elevator car and counterweight move upward and downward within the elevator shaft on rails.
Conventional elevators also include one or more emergency braking systems to prevent the elevator car from ascending or descending too quickly in the event of a system failure such as a broken cable. The brakes may be applied in a variety of locations. For example, some brakes are mounted between the elevator car and the rails on which the elevator car rides. These brakes produce rough braking and may inflict damage to the elevator car rails. Further, these brakes are difficult to install in existing elevators. Another type of brake apply a braking force directly to the cables in the elevator. This type of brake may inflict damage to the cables (requiring extensive inspection and downtime for the elevator) and is difficult to install in existing elevators. Another type of conventional brake includes a disc mounted coaxially with the elevator sheave and an actuator that applies a braking force to one side of the disc while another type of conventional brake includes calipers that apply a braking force to either side of a disc or to a shaft. These type of brake requires modifications in existing elevators and the caliper brakes are also generally limited to use with discs of certain widths. Yet another type of conventional brake applies a braking force to the outer or inner diameter of the sheave. This type of brake also requires extensive modifications in existing elevators (e.g., machining flats or bosses on the sheave surface) and the friction material in the brake must often be specially adapted for use with the sheave. U.S. Pat. No. 4,923,055 discloses a brake including two calipers that apply a braking force to either longitudinal end of the sheave. This brake is also unsuitable for use with existing elevators, however, as the brake actuator relies on bosses machined into an inner diameter at one end of the sheave.
Conventional elevator brakes therefore have significant disadvantages. In particular, conventional elevator brakes-while suitable for use in new elevators—are not adapted for ease of installation and use in existing elevators. The inventors herein have recognized a need for an elevator brake that will minimize and/or eliminate one or more of the above-identified deficiencies.